Thermoelectric element comprising a contact structure and method of making the contact structure

ABSTRACT

An induction heating system can comprise a furnace chamber comprising a non-magnetic and non-conductive furnace wall; at least one induction heating coil surrounding an outer side of the furnace wall in a length direction (z) of the furnace chamber; and a holding and pressing construction. The holding and pressing construction can be designed to hold an arrangement to be placed within the furnace chamber, and the holding and pressing construction can apply a pressure on a proximal end and a distal end of the arrangement in the length direction of the chamber.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application No. 63/053,429, entitled “THERMOELECTRIC ELEMENTCOMPRISING A CONTACT STRUCTURE AND METHOD OF MAKING THE CONTACTSTRUCTURE,” by Aruna R. DEDIGAMA et al., filed Jul. 17, 2020, whichapplication is assigned to the current assignee hereof and incorporatedherein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to an induction heating system,specifically to an induction heating system adapted to form a contactstructure of a thermoelectric element.

BACKGROUND

Thermoelectric elements are known for converting heat energy toelectrical energy. Typically, a temperature gradient is formed betweentwo opposite sides of a thermoelectric element, and the heat flow fromthe hot side to the cold side creates a voltage that can be trapped foroperating an electrical device or being stored. In order to makeefficient thermoelectric elements, an important aspect is a stablecontact structure between the thermoelectric material and the heatsource/cooling device which can survive tough mechanical and thermalconditions.

There exists a need to improve the contact structure of thermoelectricelements to increase the efficiency, stability, and life-time ofthermoelectric elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art, byreferencing the accompanying drawings.

FIG. 1 includes an illustration of a thermoelectric element according toone embodiment.

FIG. 2 includes a scheme of a method of forming a contact structureaccording to one embodiment.

FIG. 3A includes an illustration of a step of the process of making acontact structure according to one embodiment.

FIG. 3B includes an illustration of a step of the process of making acontact structure according to one embodiment.

FIG. 3C includes an illustration of a step of the process of making acontact structure according to one embodiment.

FIG. 3D includes an illustration of a thermoelectric element includingtwo contact structures which was arrived from the intermediatestructures shown in FIGS. 3A-3C according to one embodiment.

FIG. 4 includes an illustration of a thermoelectric element according toone embodiment.

FIG. 5 includes an optical image of a crosscut of a thermoelectricelement according to one embodiment.

FIG. 6 includes an optical image of a crosscut of a thermoelectricelement according to one embodiment.

FIG. 7 includes an illustration of an arrangement configured forinduction heating using an induction heating system according to oneembodiment.

FIG. 8 includes an illustration of an induction heating system accordingto one embodiment.

FIG. 9 includes an illustration of an induction heating system accordingto one embodiment.

FIG. 10A includes an optical microscope image of a cross-cut of aportion of a thermoelectric element according to one embodiment.

FIG. 10B includes a larger magnification of the image shown in FIG. 10Aaccording to one embodiment.

FIG. 11A includes an optical microscope image of a cross-cut of aportion of a thermoelectric element according to one embodiment.

FIG. 11B includes a larger magnification of the image shown in FIG. 11Aaccording to one embodiment.

DETAILED DESCRIPTION

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus.

As used herein, and unless expressly stated to the contrary, “or” refersto an inclusive-or and not to an exclusive-or. For example, a conditionA or B is satisfied by any one of the following: A is true (or present)and B is false (or not present), A is false (or not present) and B istrue (or present), and both A and B are true (or present).

Also, the use of “a” or “an” are employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one or at least one and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Various embodiments of the present disclosure will now be described, byway of example only, with reference to the accompanying drawings.

In one embodiment, the present disclosure is directed to athermoelectric element comprising a thermoelectric body, a first contactstructure (CS01), and a second contact structure (CS02). As illustratedin the embodiment of FIG. 1, the first contact structure (CS01) cancomprise at least one first porous metal structure (11) being at leastpartially embedded in a first outer region (13) of the thermoelectricbody (14), and at least one first metal layer (12) overlying an outersurface (18) of the first outer region (13) and being in direct contactwith the embedded first porous metal structure (11). The second contactstructure (CS02) on the opposite side of the thermoelectric element mayhave the same structure as the first contact structure (CS01), includingat least one second porous metal structure (16) embedded within a secondouter region (15) of the thermoelectric body (14) and at least onesecond metal layer (17) overlying an outer surface (19) of the secondouter region (15), and wherein the at least one second metal layer (17)can be in direct contact with the at least one second porous metalstructure (16). In another aspect, not shown and further describedbelow, the second contact structure (CS02) can have a differentstructure as the first contact structure (CS01).

As used herein, the term “outer region” of the thermoelectric body (14),if not stated otherwise, relates to the first and/or second outerregion(s) (13, 15) of the thermoelectric body (14), which can betransformed to a softened outer region by heating to allow embedding theat least one first and/or second porous metal structure (11, 16). Theouter region starts from the outer surface (18 and/or 19) of thethermoelectric body towards the center of the body (z-direction) havinga thickness of at least 40 microns and not greater than 400 microns. Ina certain aspect, a thickness ratio of the outer region on one side ofthe thermoelectric body (18 or 19) to the total thickness of thethermoelectric body (14) can be a range from 1:5 to 1:500.

As used herein, the term “porous metal structure” relates to a highlyporous metal construct, which can be in embodiments a metal mesh or ametal foam.

The present disclosure is further directed to a method of forming acontact structure on a thermoelectric body. In one embodiment, asillustrated in FIG. 2, the method can comprise: providing athermoelectric body (21); heat treating an outer region of thethermoelectric body (22), wherein heat treating can cause partialmelting of the outer region and forming of a softened outer region;embedding at least one porous metal structure within the softened outerregion (23); cooling and solidifying the softened outer region (24); andapplying at least one metal layer overlying the outer region (25),wherein the at least one metal layer can be in direct contact with theat least one partially embedded porous metal structure.

FIG. 3A illustrates an embodiment wherein two porous metal structures(31 a), for example, two metal meshes, can be positioned directly nextto the outer surface (38 a) of a first outer region (33) of thethermoelectric body (32 a); and two porous metal structures (31 b), maybe positioned next to the outer surface (39 a) of a second outer region(34), of the thermoelectric body (32 a).

In other embodiments, the at least one porous metal structure caninclude a total of one to five porous metal structures, such as oneporous metal structure, or two porous metal structures, or three porousmetal structures, or four porous metal structures, or five porous metalstructures. In a certain particular aspect, the at least one porousmetal structure may include two porous metal structures.

The at least one porous metal structure can have a thickness of at least40 microns, or at least 50 microns, or at least 70 microns, or at least80 microns, or at least 100 microns, or at least 120 microns. In anotheraspect, the thickness of the at least one metal mesh may be not greaterthan 500 microns, or not greater than 300 microns, or not greater than250 microns, or not greater than 200 microns, or not greater than 150microns, or not greater than 120 microns, or not greater than 100microns. As used herein, the thickness of the at least one porous metalstructure relates to the combined thickness of all porous metalstructures together before embedding within the thermoelectric body.

In one aspect, the at least one porous metal structure can be a metalmesh. In a particular aspect, the metal mesh may be a nickel mesh. Themetal mesh can have a mesh size of at least 100 mesh, or at least 150mesh, or at least 200 mesh, or at least 300 mesh. In a further aspect,the mesh size may be not greater than 460 mesh, or not greater than 400mesh or not greater than 350 mesh or not greater than 300 mesh. In afurther aspect, the metal mesh can have a mesh count of at least 100mesh/inch, or at least 200 mesh/inch, or at least 350 mesh/inch. In yetanother aspect, the mesh count may not be greater than 460 mesh/inch, or400 mesh/inch, or 360 mesh/inch.

In yet a further aspect, the metal mesh can have a wire diameter of atleast 15 microns, or at least 20 microns, or at least 25 microns, or atleast 30 microns. In another aspect, the wire diameter of the metal meshmay be not greater than 50 microns, or not greater than 40 microns, ornot greater than 35 microns.

In another aspect, the at least one porous metal structure can be ametal foam. In a particular aspect, the metal foam can be a nickel foam.

In a certain aspect, the metal foam can have a porosity between 10 vol %to 95 vol %, such as at least 15 vol %, at least 20 vol %, at least 25vol %, at least 30 vol %, at least 35 vol %, at least 40 vol %, or atleast 50 vol %. In another aspect, the porosity of the metal foam may benot greater than 90 vol %, or not greater than 80 vol %, or not greaterthan 70 vol %, or not greater than 60 vol %.

The average pore size of the metal foam can range from at least 0.01 mmto not greater than 0.3 mm, such as at least being 0.02 mm, or at least0.05 mm, or at least 0.1 mm and not greater than 0.25 mm, or not greaterthan 0.2 mm, or not greater than 0.15 mm.

In a further aspect, the metal foam can consist essentially of nickeland may have a density of at least 1.5 g/cm³, or at least 2.0 g/cm³, orat least 2.5 g/cm³, or at least 3.0 g/cm³. In another aspect, thedensity of the foam may be not greater than 3.5 g/cm³, or not greaterthan 3.3 g/cm³, or not greater than 3.0 g/cm³. In a particular aspect,the density of the nickel foam can be at least 2.5 g/cm³ and not greaterthan 3.5 g/cm³.

In a certain particular aspect, the metal foam can be a nickel foam andmay have a thickness between 70 microns and 120 microns and a densitybetween 2.5 g/cm³ to 3.5 g/cm³.

In a further aspect, the metal foam can be a nickel foam having atensile strength in a length direction of at least 1.25 N/mm2, and inits width direction of at least 1.0 N/mm2.

As used herein, the parameters of the metal mesh or metal foam, areparameters before embedding the mesh or foam within the thermoelectricbody and these parameters can vary to a certain degree after embedding.

In another embodiment of the method, the thermoelectric body can includebefore heat treating at least one provisional metal layer (also calledherein “sacrificial metal layer”) directly overlying the outer region ofthe thermoelectric body. The at least one provisional metal layer canreact during induction heating with the material of the thermoelectricbody and may thereby be consumed. In a certain aspect, the inclusion ofsuch at least one provisional metal layer can further enhance thelifetime of the contact structure of the thermoelectric element.

In one aspect, the at least one provisional metal layer can include thesame type of metal as the nickel meshes to be embedded within the outerregions of the thermoelectric body. In a certain aspect the at least oneprovisional metal layer may include a first provisional nickel layerdirectly overlying an outer region of the thermoelectric body, and asecond provisional nickel layer directly overlying the first provisionalnickel layer. The first provisional nickel layer can have a thickness ofat least 20 nm and not greater than 1 micron, while the second nickellayer may have a thickness of at least 1 micron and not greater than 6microns. In a certain aspect, the first provisional nickel layer canhave a higher stress than the second provisional nickel layer. In aparticular embodiment, the at least one provisional metal layer caninclude two provisional nickel layers and a material of thethermoelectric body may include PbTe.

In one embodiment, heat treating of the outer region of thethermoelectric body can be conducted by heating this region close to amelting temperature of the material of the thermoelectric body and for atime that only the outer region is submitted to partial melting andsoftening and to forming a softened outer region. In one aspect, heattreating can be conducted by heating the outer region to a maximumtemperature, wherein the maximum temperature may be at least the meltingtemperature of the thermoelectric material. In a certain aspect, themaximum temperature during heat treating may be not greater than 100° C.above the melting temperature of the material of the thermoelectricbody, such as not greater than 50° C., or not greater than 30° C. or notgreater than 20° C., or not greater than 10° C.

In one embodiment, heat treating of the outer region of thethermoelectric body can be conducted by induction heating of the porousmetal structure positioned next to the outer region. By placing theporous metal structure directly next to the outer region of thethermoelectric body, the heat generated within the porous metalstructure during induction heating may function as a direct heat sourcefor partially melting and softening the outer region of thethermoelectric body.

Induction heating can have the advantage of reaching the desired maximumtemperature within a very short time and allowing to control the heattreatment in a time interval of even 5 to 10 seconds. Such short andcontrolled heating can allow a melting of only a defined outer region ofthe thermoelectric body suitable for embedding the at least one metalmesh, while the majority of the thermoelectric body can remain solid andmaintain its structure.

In one aspect, the induction heating can be performed that a temperatureof the heating element positioned at a defined distance next to theporous metal structures, herein also called tooling temperature, is atleast 300° C. and not greater than 500° C. Such tooling temperaturerange can convert to a temperature within the porous metal layers fromabout 600° C. to about 1100° C.

In a particular embodiment, the heat treatment can include heating to amaximum tooling temperature of at least 320° C., or at least 340° C., orat least 360° C., or at least 380° C., or at least 400° C., or at least420° C., or at least 440° C. In another embodiment, the maximum toolingtemperature of the heat treatment may be not greater than 440° C. or notgreater than 420° C. or not greater than 400° C. or not greater than380° C. or not greater than 360° C. or not greater than 340° C.

In a particular aspect, induction heating can comprise two steps: 1) afirst heat treatment, wherein the tooling (induction coil) can be heatedto a lower preheat tooling temperature in a range of between 110° C. to150° C. and maintained at this temperature for about 40-200 seconds,followed 2) by a second heat treatment, wherein the tooling can beheated to a high tooling temperature T_(max) and maintained at T_(max)for about 1-20 seconds, followed by free cooling. The T_(max)temperature of the tooling can be selected that it corresponds totemperature within the porous metal structure being close to the meltingtemperature of the material of the thermoelectric body.

In one aspect, the induction heating can cause a heating of the porousmetal structures to at least 350° C., or at least 400° C., or at least500° C., or at least 600° C., or at least 630° C., or at least 650° C.,or at least 700° C., or at least 750° C., or at least 800° C., or atleast 900° C. In another aspect, the temperature of the porous metalstructures may be not greater than 1100° C., or not greater than 1000°C., or not greater than 950° C., or not greater than 920° C., or notgreater than 900° C., or not greater than 850° C., or not greater than800° C., or not greater than 750° C., or not greater than 700° C., ornot greater than 650° C.

To assure that only the outer region of the thermoelectric body ismelted, induction heating at the maximum tooling temperature T_(max) canbe conducted for at least 5 seconds and not greater than 20 seconds, orat least 5 seconds and not greater than 15 seconds, or at least 5seconds and not greater than 12 seconds, or at least 5 seconds and notgreater than 10 seconds.

In one embodiment, the induction heating during the second heattreatment can be regulated by measuring the electric current flowthrough the induction coil circuit. In a certain aspect, the second heattreatment can be terminated when detecting an increase of the electriccurrent by about 3-5 percent compared to the electric current measuredwhen reaching the maximum tooling temperature, herein also called“A_(Tmax-b),” i.e., the electric current at the beginning of the secondheat treatment maximum temperature.

Accordingly, for controlling the time during the second heat treatment,the following equation can be applied: A_(S)=A_(Tmax-b)+AA, with A_(S)being the current when stopping the induction heating, A_(Tmax-b) beingthe electric current measured when reaching the maximum temperature ofthe second heat treatment, and AA the current increase of 3-5% based onA_(Tmax-b). Not being bound to theory, the increase in the electriccurrent in the induction heating coil circuit by 3-5% can be anindication that the porous nickel structure at least partially reactedwith the material of the thermoelectric body, which may cause a drop inthe electromagnetic permeability of the nickel structure, and therebycan cause an increase in the electric current of the induction heatingcoil.

During heat treatment at the maximum temperature, the outer region ofthe thermoelectric body can be melted and a softened outer region can beformed, which allows embedding of the at least one porous metalstructure within the softened outer region. As used herein, the term“softened” is interchangeably used with “at least partially melted” andrefers to the stage that the metal mesh can be embedded within the outerregion.

In one aspect, embedding the at least one porous metal structure withinthe softened outer region can be conducted by applying a pressure on theat least one porous metal structure during or after induction heating.In a certain aspect, the applied pressure on the porous metal structurecan be at least 5 psi, or at least at least 8 psi, or at least 10 psi.In another certain aspect, the pressure may be not greater than 15 psi,or not greater than 12 psi, or not greater than or not greater than 10psi.

FIG. 3B illustrates an embodiment wherein the at least one first porousmetal structure (31 a) and the at least one second porous metalstructure (31 b) shown in FIG. 3A are completely embedded within thefirst outer region (33) and the second outer region (34) of thethermoelectric body (32 a), respectively.

In another embodiment, the at least one porous metal structure can beonly partially embedded within the outer region of the thermoelectricbody. In certain aspects, at least 80 vol % of the porous metalstructure can be embedded within the outer region, or at least 85 vol %,or at least 90 vol %, or at least 95 vol %, or at least 98 vol %. Inother certain aspects, not greater than 99 vol % of the porous metalstructure may be embedded, or not greater than 98 vol %, or not greaterthan 95 vol %, or not greater than 90 vol %.

If the at least one porous metal structure is completely embedded withinthe thermoelectric body, polishing can be conducted to remove thematerial of the thermoelectric body which covers the at least one porousmetal structure, until portions of the at least one porous metalstructure reach the outer surface of the thermoelectric body. FIG. 3Cillustrates the thermoelectric body of FIG. 3B after polishing, whereinthe at least one first porous metal structure (31 a) and the at leastone second porous metal structure (31 b) are level with the polishedouter surface (38 p) and the polished outer surface (39 p), of thepolished thermoelectric body (32 p), respectively.

FIG. 3D illustrates an embodiment, wherein on each outer surface of thepolished thermoelectric body shown in FIG. 3C furthermore two metallayers are applied: a first metal layer (35 a) being in direct contactwith the at least one first embedded porous metal structure (31 a), anda second metal layer (36 a) directly overlying the first metal layer (35a). On the opposite side, a first metal layer (35 b) being in directcontact with the at least one second porous metal structure (31 b), anda second metal layer (36 b) directly overlying the first metal layer (35b). As further illustrated in FIG. 3D, the first contact structure(CS01) can include two metal meshes of the at least one first porousmetal structure (31 a), the first metal layer (35 a) and the secondmetal layer (36 a); and the second contact structure (CS02) on theopposite side may include the two metal meshes of the at least onesecond porous metal structure (31 b), the first metal layer 35 b and thesecond metal layer 36 b.

Non-limiting examples of the at least one porous metal structure and ofthe at least one metal layer can be nickel, copper, titanium, palladium,cobalt, molybdenum, iron, aluminum, or metal alloys. As used herein, theterms “porous metal structure” or “metal layer” mean that the majorityof the material is metal, but other non-metal elements or additives maybe also included to a minor content of up to 20 wt %, for example,phosphorus, carbon, silicon, nitrogen, boron, or any combinationthereof. In a certain aspect, the at least one porous metal structureand the at least one metal layer can include the same metal. In aparticular embodiment, the at least one porous metal structure and theat least one metal layer may include nickel. In a certain particularaspect, the at least one porous metal structure and the at least onemetal layer may consist essentially of nickel. As used herein,consisting essentially of nickel means having a nickel content of atleast 98 wt %. In a particular certain aspect, the at least one porousmetal structure and/or at least one metal layer can have a nickelcontent of at least 99.0 wt %, or at least 99.5 wt % or at least 99.9 wt%.

In one embodiment, the first metal layer (35 a, 36 a) can have a lowerthickness than the second metal layer (35 b, 36 b). In a certain aspect,a thickness ratio of the first metal layer to the second metal layer canbe not greater than 0.1, such as not greater than 0.05, or not greaterthan 0.033, or not greater than 0.025, or not greater than 0.02, or notgreater than 0.017, or not greater than 0.014.

In one aspect, the average thickness of the first metal layer (35 a, 36a) can be at least 10 nm, or at least 30 nm, or at least or at least 50nm, or at least 100 nm, or at least 150 nm, or at least 200 nm. Inanother aspect, the average thickness of the first metal layer may benot greater than 2000 nm, or not greater than 1500 nm, or not greaterthan 1000 nm, or not greater than 800 nm, or not greater than 500 nm, ornot greater than 300 nm. The average thickness of the first metal layercan be a value between any of the minimum and maximum values notedabove.

In a further aspect, the average thickness of the second metal layer (35b, 36 b) can be at least 3 microns, or at least 5 microns, or at least10 microns, or at least 50 microns, or at least 80 microns, or at least100 microns, or at least 150 microns. In another aspect, the averagethickness of the second metal layer may be not greater than 200 microns,or not greater than 180 microns, or not greater than 160 microns, or notgreater than 140 microns, or not greater than 120 microns. The averagethickness of the second metal layer can be a value between any of theminimum and maximum values noted above.

In one embodiment, the first metal layer (35 a, 36 a) and the secondmetal layer (35 b, 36 b) can consist essentially of nickel, herein alsocalled first nickel layer and second nickel layer, wherein a stress ofthe second nickel layer (35 b, 36 b) may be lower than a stress of thefirst nickel layer (35 a, 36 a). In one aspect, the stress of the firstnickel layer can be at least 70 MPa, or at least 100 MPa, or at least150 MPa, or at least 300 MPa, or at least 400 MPa, or at least 500 MPa,or at least 600 MPa, or at least 650 MPa, or at least 700 MPa, or atleast 750 MPa, or at least 800 MPa. In a further aspect, the stress ofthe first nickel layer can be not greater than 1500 MPa, or not greaterthan 1300 MPa, or not greater than 1100 MPa.

In a further aspect, the stress of the second nickel layer can be atleast 5 MPa, or at least 10 MPa, or at least 50 MPa, or at least 100MPa, or at least 150 MPa. In yet another aspect, the stress of thesecond nickel layer may be not greater than 630 MPa, or not greater than600 MPa, or not greater than 550 MPa, or not greater than 500 MPa, ornot greater than 450 MPa, or not greater than 400 MPa, or not greaterthan 350 MPa, or not greater than 300 MPa, or not greater than 150 MPa,or not greater than 100 MPa, or not greater than 80 MPa.

In a certain aspect, the stress of the second nickel layer can be atleast 50 percent lower than a stress of the first nickel layer, such asat least 70 percent lower, at least 100 percent lower, at least 150percent lower, or at least 200 percent lower.

In one aspect, the first metal layer (35 a, 36 a) and the second metallayer (35 b, 36 b) can be applied by electroplating. It is appreciatedthat any other process known in the art for depositing a metal layer canbe also used, for example, electroless metal plating, or dip coating, orchemical vapor deposition.

In a particular aspect, the first metal layer (35 a, 36 a) and thesecond metal layer (35 b, 36 b) can be formed by conductingelectroplating of nickel. In order to produce nickel layers withdifferent phases, electroplating can be conducted at different pHranges. In one aspect, the first nickel layer can be formed byelectroplating of nickel at a pH between 7.5 and 8.5, while the secondnickel layer may be formed by electroplating of nickel at a pH between3.5 and 4.5. In a particular aspect, the first nickel layer can beformed by electroplating nickel at a pH between 7.70 and 8.06, and thesecond nickel layer may be applied by nickel electroplating at a pHbetween 3.6 and 4.3.

The thermoelectric body of the thermoelectric element of the presentdisclosure can comprise any thermoelectric material suitable forconverting thermal energy to electrical energy.

In one aspect, the material of the thermoelectric body can be an n-typesemiconductor material. In a particular aspect, the n-type semiconductormaterial can include lead telluride (PbTe).

In another aspect, the thermoelectric body can include a p-typesemiconductor material. In a certain aspect, the p-type semiconductormaterial can be a material including tellurium/antimony/germanium/silver(Te/Sb/Ge/Ag), herein also called “TAGS.”

In a further embodiment, the thermoelectric element of the presentdisclosure can comprise a thermoelectric body, a first contact structuresecond (CS01), and a second contact structure (CS02), wherein the firstcontact structure may be the same as described above, but the secondcontact structure (CS02) may be different than the first contactstructure (CS01). In one aspect, the second contact structure mayinclude at least one metal layer directly overlying the thermoelectricbody and no embedded porous metal structure. In a certain aspect, asillustrated in FIG. 4, the second contact structure (CS02) can be acombination of four metal layers (46 a, b, c, and d) including the samemetal. In a certain aspect, the four metal layers can all includenickel. The four nickel layers can have a first nickel layer (46 a) anda second nickel layer (46 b), which can correspond to the first nickellayer (45 a) and the second nickel layer (45 b) of the first contactstructure (CS01), as also described above for varying thickness andstress. The third nickel layer (46 c) and fourth nickel layer (46 d) maybe a repetition of the first nickel layer (46 a) and the second nickellayer (46 b). If a four nickel layer structure is applied as the secondcontact structure, induction heating can be conducted after applying thesecond nickel layer (46 b) and before depositing the third nickel layer(46 c). Induction heating can cause a partial melting of the outerregion of the thermoelectric body and a stronger bond of the first andsecond nickel layers to the thermoelectric body. A four nickel layerstructure as a second contact structure can be applied on the intended“cold side” of a thermoelectric body, which means across the side of thebody which will be closest to a heat source for forming a thermalgradient.

The use of two different contact structures may be considered in anembodiment wherein between the second contact structure (CS02) and thethermoelectric body (42), a further functional layer (44) may beincluded. For example, the functional layer (44) can be anothersemiconductor layer or a barrier layer. In a non-limiting embodiment,the functional layer (44) can be the same type of semiconductor as thethermoelectric body, wherein the two semiconductors may differ by n-typedoping and p-type doping. In another embodiment, the functional layercan be a different type of semiconductor material, such as that thethermoelectric body is a p-type semiconductor and the additionalfunctional layer can be an n-type semiconductor, or that thethermoelectric body may be an n-type semiconductor and the additionalfunctional layer can be a p-type semiconductor. In a certain aspect, thethermoelectric body (42) may be an n-type PbTe material and the otherfunctional layer (44) can be a layer of Iridium (Ir) or Titanium (Ti).In another certain aspect, the thermoelectric body (42) can be a TAGSmaterial and the functional layer (44) can be a tantalum (Ta) layer.

In another aspect, the functional layer (44) can also be included in thethermoelectric element of the present disclosure if the first contactstructure (CS01) and the second contract structure (CS02) are the same.

In a further embodiment of the present disclosure, an outer metal layercan be applied on the first and/or second contact structure, wherein theouter metal layer can include a different metal than the metal layers ofthe first and/or second contact structure. In one aspect, the outermetal layer can be a layer including silver, herein also called silverlayer. In a certain aspect, the silver layer can be applied byelectro-deposition from a silver salt solution.

In a particular embodiment, forming the first and a second contactstructure described above on a thermoelectric body can compriseassembling an arrangement, and subjecting the arrangement to inductionheating. In one aspect, the arrangement can include in the center thethermoelectric body, surrounded by the at least one first porous metalstructure and the at least one second porous metal structure. In aparticular aspect, the arrangement can have a layer structure of thefollowing order, as also illustrated in FIG. 7: a first heat spreadinglayer (71); a first induction heat absorber layer (22); a second heatspreading layer (73), at least one first porous metal structure (74), athermoelectric body (75), at least one second porous metal structure(76), a third heat spreading layer (77), a second induction heatabsorber layer (78), and a fourth heat spreading layer (79).

In a particular aspect, all four heat spreading layers (71, 73, 77, 79)can include the same material, for example, graphite or sapphire. Thethickness of each heat spreading layer can be from 0.2 mm to 2.5 mm.

In another aspect, the material of the first and second induction heatabsorber layers (72, 78) can be nickel, copper, or stainless-steel, andbe provided in form of a porous metal structure or a fully formed plate.In a particular aspect, the material of the heat absorber layers (72,78) may be the same as the material of the at least one first and secondporous metal structure (74, 76). The thickness of each induction heatabsorber layer can be from 0.04 mm to 2.0 mm. The selection of a certainthickness of the heat spreading layers and the heat absorber layers mayhelp to optimize the heating conditions during induction heating.

The inclusion of the first and second induction heat absorber layers(72, 78) surrounded by the head spreading layers can have the advantageof providing rapid and stable heat at both sides of the thermoelectricbody throughout the process of embedding the porous metal structures(74, 76) within the outer regions of the thermoelectric body. While theporous metal structures (74, 76) can contribute initially to the heatingof the first and second outer regions of the thermoelectric body, theeffectiveness of the heating decreases during the actual embedding ofthe metal meshes. The heat absorber layers (72, 78) surrounded by theheat spreading layers (71, 73, 77, 79) can further help to apply an evenpressure throughout the area of the at least one first and at least onesecond porous metal structure (74, 76) for embedding the porousstructures within the outer regions of the thermoelectric body.

An embodiment of a heating system configured for induction heating theabove-described arrangement such that the at least one first porousmetal structure and the at least one second porous metal structure canbe embedded within the outer regions of the thermoelectric body isillustrated in FIG. 8.

The heating system (80) can include a furnace chamber (81) having afurnace wall (82) made of a non-conductive and non-magnetic material. Ina certain embodiment, the furnace wall (82) can have a circular shapeforming a cylindrical furnace chamber (81). At least one inductionheating coil (83) can surround the furnace wall (82) from the outside.In a certain aspect, the distance (d₁) of the induction heating coil(83) to the furnace wall (82) can be adjusted and may vary from 0 mm to10 mm. The distance (d₁) is however not limited to a range of 0 to 10 mmand can be up to 100 mm or greater for other applications of the heatingsystem (80). In another certain aspect, the induction heating coil (83)can be hollow and cold air may flow through the hollow coil duringoperation of the heating system, specifically during induction heatingand cooling of the coil. A non-limiting example of a flow rate of theair can be 0.5 l/min.

In one aspect, the cold air can enter the coil at a bottom entrance (84a) and leave it at a top exit (84 b). The heating system (80) canfurther include a holding and pressing construction (85) which can holdand apply a desired pressure on an inserted arrangement (86) if placedwithin the furnace chamber (81). The holding and pressing construction(85) can include movable pedestals which can be attached to the outertop (86 a) and outer bottom (86 b) of the arrangement (86) and may bedesigned to apply a desired pressure in a length direction (z) from bothsides of the arrangement in an upward and downward direction,respectively. The holding and pressing construction (85) can ensure thatthe arrangement (86) is held together under a certain pressure whichalso allows embedding of the at least one first porous metal structureand the at least one second porous metal structure within the first andsecond outer regions of the thermoelectric body after softening theseregions, respectively. In one aspect, the pressure applied by theholding and pressing construction of the arrangement can be in a rangeof 5 psi to 15 psi.

The furnace chamber (81) can further include a gas inlet (88 a) and agas outlet (88 b) for allowing a gas flow through the furnace chamber,for example, when working under oxygen-free conditions. In one aspect,the gas flowing through the chamber can be an argon gas, also called aforming gas, containing 95% argon and 5% hydrogen. In a certain aspect,the argon gas can flow through the furnace at a flow rate of at least 40ml/min, or at least 50 ml/min, or at least 70 ml/min, or at last 100ml/min at a corresponding volume of the furnace of about 100 cm³. Inanother certain aspect, the flow rate may be not greater than 150ml/min, or not greater than 120 ml/min.

A temperature sensor (89) may be further placed within the chamber (81)for controlling and regulating the temperature of the at least oneporous metal structure contained within an inserted arrangement (86). Inone aspect, the temperature sensor can be an IR temperature sensor. TheIR temperature sensor can measure the temperature of the outer heatspreading layers (71 or 79), which can provide an indirect relativetemperature indication of the porous metal structures (74, 76) and theouter regions of the thermoelectric body (75).

The induction heating system can further comprise a control unit, forexample, a computer, to coordinate the induction heating. In oneembodiment, as illustrated in FIG. 9, the induction heating system (90)can include a control unit (91), which can be connected to an inductionheating device (92) and a temperature sensor (93) contained in thefurnace chamber. Based on the information obtained by the temperaturesensor and the material type of thermoelectric body, the control unitcan determine the needed current frequency and time for operating theinduction heating device (92) connected to the induction coils (94). Inone aspect, the applied current frequency can be at least 80 kHz, or atleast 100 kHz, or at least 200 kHz. In another aspect, the currentfrequency may be not greater than 10 MHz, or 1 MHz, or 500 kHz. Thecontrol unit (91) may further regulate and initiate the cooling afterthe induction heating, for example, initiating the flow of cool airthrough the hollow induction spirals. In a further aspect, the controlunit can further regulate the pressure applied by the holding andpressing construction on an arrangement.

In another aspect, the electric current flowing through the inductioncoils (94) can be measured and sent to the control unit. The controlunit can be configured that at a certain maximum current flow, theinduction heating is stopped or interrupted. For example, as describedabove, the exact current drawn by the induction heating circuit of theat least one induction coil (94) can be measured with an ampere meter(not shown) and the ampere meter may be connected to the control unit.The control unit may record any changes of the electric current from thebeginning of the second heat treatment (T_(max-b)) and can initiate at acurrent increase of 3-5% the induction heating to be stopped bycommunication with the induction heating device. For example, thecontrol unit may register a current of 9 A at the beginning of thesecond heat treatment when reaching T_(max) and can initiate to stop theinduction heating when the current reaches 9.3 A.

The induction heating device can operate during the two temperaturetreatments such that during the first heat treatment, a defined inputpower to the induction coil circuit can be regulated via a duty cycle(for example, the power can be ON for 0.125 seconds and OFF for 0.125seconds to maintain the temperature at 160° C., which is called herein a50% duty cycle). During the second temperature heat treatment, the dutycycle can be changed to 100%, which means the selected power is ON allthe time, and the current increase to evaluate the termination of theheating can be observed and monitored.

Controlling the increase in the current flow in the at least oneinduction heating coil circuit can increase the sensitivity of themethod by stopping the heating exactly at the appropriate time that themetal porous structure is embedded within the thermoelectric body andmay prevent overheating and unnecessary damage of the thermoelectricbody by excessive melting. The method of observing the current can bemore sensitive than measuring the temperature with the IR sensor sincethe IR sensor can only indirectly provide information about the actualtemperature at the outer region of the thermoelectric body by measuringthe temperature of the outer heat spreading layer.

The thermoelectric element of the present disclosure can be adapted forconverting heat energy from a heat source to electrical energy, whereinthe heat source can have a temperature in a range of at least 100° C.and not greater than 600° C. Furthermore, a plurality of thermoelectricelements of the present disclosure can be assembled to a thermoelectricdevice for converting heat energy to electrical energy on a largerscale.

As further demonstrated in the examples, the above-described method canproduce thermoelectric elements with strong and high stress toleratingcontact structures which can provide a long lifetime of thethermoelectric elements. Not being bound to theory, the embedded metalmeshes within the outer regions of the thermoelectric body can provide areinforced structure as a basis for a strong hold of the applied metallayers of the contact structure, while the thermoelectric properties ofthe thermoelectric body can be maintained.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described herein. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Embodiments may be in accordance with any one or moreof the embodiments as listed below.

EMBODIMENTS

Embodiment 1. A thermoelectric element comprising: a thermoelectricbody, a first contact structure, and a second contact structure, wherein

-   -   the first contact structure comprises at least one first porous        metal structure and at least one metal layer, wherein the at        least one first porous metal structure is at least partially        embedded within a first outer region of the thermoelectric body,        and the at least one metal layer is overlying an outer surface        of the first outer region of the thermoelectric body and in        direct contact with the at least one metal mesh.

Embodiment 2. The thermoelectric element of embodiment 1, wherein the atleast one metal layer comprises a first metal layer and a second metallayer, and wherein each of the at least one first porous metalstructure, the first metal layer, and the second metal layer include thesame metal.

Embodiment 3. The thermoelectric element of embodiment 2, wherein eachof the at least one first porous metal structure, the first metal layer,and the second metal layer comprise nickel.

Embodiment 4. The thermoelectric element of embodiments 2 or 3, whereineach of the at least one first porous metal structure, the first metallayer, and the second metal layer consist essentially of nickel.

Embodiment 5. The thermoelectric element of any one of the precedingembodiments, wherein the at least one first porous metal structurecomprises two porous metal structures.

Embodiment 6. The thermoelectric element of any one of the precedingembodiments, wherein the at least one first porous metal structure has athickness of at least 30 microns and not greater than 175 microns.

Embodiment 7. The thermoelectric element of any one of the precedingembodiments, wherein at least 90 vol % of the at least one first porousmetal structure is embedded within the first outer region of thethermoelectric body.

Embodiment 8. The thermoelectric element of embodiment 7, wherein the atleast one first porous metal structure is completely embedded within thefirst outer region of the thermoelectric body.

Embodiment 9. The thermoelectric element of any one of the precedingembodiments, wherein the at least one first porous metal structureincludes at least one metal mesh, or at least one metal foam, or anycombination thereof.

Embodiment 10. The thermoelectric element of embodiment 9, wherein theat least one first porous metal structure includes at least one metalmesh.

Embodiment 11. The thermoelectric element of embodiment 10, wherein theat least one metal mesh has a mesh size of at least 100 mesh and notgreater than 400 mesh.

Embodiment 12. The thermoelectric element of embodiment 9, wherein theat least one porous metal structure includes at least one metal foam.

Embodiment 13. The thermoelectric element of embodiment 12, wherein theat least one metal foam comprises a porosity of at least 20 vol % andnot greater than 95 vol %, and an average pore size from 0.02 mm to 0.25mm.

Embodiment 14. The thermoelectric element of embodiments 12 or 13,wherein the at least one metal foam has a density of at least 1.5 g/cm³,or at least 2.0 g/cm³, or at least 2.5 g/cm³, or at least 3.0 g/cm³, andnot greater than 3.5 g/cm3, or not greater than 3.3 g/cm3, or notgreater than 3.0 g/cm³.

Embodiment 15. The thermoelectric element of any one of embodiments2-14, wherein the first metal layer has a different stress than thesecond metal layer.

Embodiment 16. The thermoelectric element of embodiment 15, wherein astress of the first metal layer is at least 70 MPa, such as at least 150MPa, or at least 300 MPa, or at least 450 MPa, or at least 650 MPa, suchas at least 700 MPa, or at least 750 MPa, or at least 800 MPa, or atleast 850 MPa, or at least 900 MPa, or at least 1000 MPa, and notgreater than 1500 MPa, or not greater than 1300 MPa, or not greater than1100 MPa; and a stress of the second metal layer is at least 5 MPa, orat least 10 MPa, or at least 50 MPa, or at least 100 MPa, and notgreater than 600 MPa, such as not greater than 550 MPa, or not greaterthan 500 MPa, or not greater than 450 MPa, or not greater than 400 MPa,or not greater than 350 MPa, or not greater than 300 MPa, or not greaterthan 150 MPa, or not greater than 100 MPa, or not greater than 80 MPa.

Embodiment 17. The thermoelectric element of any one of embodiments2-16, wherein a thickness ratio of the first metal layer to the secondmetal layer is not greater than 0.1, such as not greater than 0.05, notgreater than 0.033, not greater than 0.025, not greater than 0.02, notgreater than 0.017, or not greater than 0.014.

Embodiment 18. The thermoelectric element of any one of embodiments2-17, wherein an average thickness of the first metal layer is at least10 nm or at least 30 nm or at least or at least 50 nm or at least 100nm, or at least 150 nm or at least 200 nm.

Embodiment 19. The thermoelectric element of any one of embodiments2-18, wherein an average thickness of the first metal layer is notgreater than 2000 nm or not greater than 1500 nm or not greater than1000 nm or not greater than 800 nm or not greater than 500 nm or notgreater than 300 nm.

Embodiment 20. The thermoelectric element of any one of embodiments2-19, wherein an average thickness of the second metal layer is at least5 microns, or at least 10 microns, or at least 50 microns, or at least80 microns, or at least 100 microns, or at least 150 microns.

Embodiment 21. The thermoelectric element of any one of embodiments2-20, wherein an average thickness of the second metal layer is notgreater than 200 microns, or not greater than 180 microns, or notgreater than 160 microns, or not greater than 140 microns, or notgreater than 120 microns.

Embodiment 22. The thermoelectric element of any one of the precedingembodiments, wherein the first contact structure further comprises anouter layer including silver.

Embodiment 23. The thermoelectric element of any one of the precedingembodiments, wherein the thermoelectric body comprises an n-typesemiconductor material.

Embodiment 24. The thermoelectric element of any one of the precedingembodiments, wherein the thermoelectric body comprises a materialincluding lead telluride (PbTe).

Embodiment 25. The thermoelectric element of any one embodiments 1-22,wherein the thermoelectric body comprises a p-type semiconductormaterial.

Embodiment 26. The thermoelectric element of embodiment 25, wherein thethermoelectric body comprises a material including Te/Sb/Ge/Ag (TAGS).

Embodiment 27. The thermoelectric element of any one of the precedingembodiments, wherein the second contact structure is the same as thefirst contact structure and the second contact structure is attached tothe thermoelectric body at a second outer region of the thermoelectricbody, the second outer region being opposite to the first outer region.

Embodiment 28. The thermoelectric element of any one of embodiments1-26, wherein the second contact structure is different than the firstcontact structure.

Embodiment 29. The thermoelectric element of embodiment 28, wherein thethermoelectric element includes an additional functional layer betweenthe second contact structure and the thermoelectric body.

Embodiment 30. The thermoelectric element of embodiment 29, wherein theadditional functional layer includes a semiconductor layer or asegmented semiconductor body.

Embodiment 31. The thermoelectric element of embodiment 29, wherein thethermoelectric body is a p-type semiconductor and the additionalfunctional layer is an n-type semiconductor.

Embodiment 32. The thermoelectric element of embodiment 29, wherein thethermoelectric body is an n-type semiconductor and the additionalfunctional layer is a p-type semiconductor.

Embodiment 33. The thermoelectric element of any one of embodiments28-32, wherein the second contact structure includes four metal layers,each of the four metal layers including nickel.

Embodiment 34. The thermoelectric element of any one of the precedingembodiments, wherein the thermoelectric element is adapted forconverting heat energy from a heat source to electrical energy, the heatsource having a temperature of at least 100° C. and not greater than650° C.

Embodiment 35. A method of forming a contact structure on athermoelectric body, comprising:

-   -   providing a thermoelectric body having a first outer region and        a second outer region, the second outer region being opposite to        the first outer region;    -   heat treating the first and/or second outer region of the        thermoelectric body, wherein heat treating causes a partial        melting of the first and/or second outer region and forming of a        softened first outer region and/or a softened second outer        region;    -   embedding at least one first porous metal structure within the        softened first outer region and/or at least one second porous        metal structure within the softened second outer region;    -   cooling and solidifying the softened first outer region and/or        the softened second outer region to form a first outer region        comprising at least one first embedded porous metal structure        and/or a second outer region comprising at least one second        embedded porous metal structure;    -   applying at least one metal layer overlying an outer surface of        the first outer region and/or at least one metal layer overlying        an outer surface of the second outer region, wherein the at        least one metal layer is in direct contact with the at least one        first embedded porous metal structure and/or the at least one        metal layer is in direct contact with the at least one second        embedded porous metal structure.

Embodiment 36. The method of embodiment 35, wherein heat treating isconducted by induction heating.

Embodiment 37. The method of embodiment 36, wherein induction heatingcomprises heating the at least one first porous metal structure to atemperature of at least the melting temperature of a material of thethermoelectric body while the at least one first porous metal structureis in direct contact with an outer surface of the outer region of thethermoelectric body.

Embodiment 38. The method of embodiments 36 or 37, wherein inductionheating comprises heating the at least one first porous metal structureto a temperature between 120° C. and 180° C. for 40-200 seconds,followed by heating the porous metal structure to a maximum temperatureof at least 350° C. and not greater than 1200° C. for a time between 5to 20 seconds.

Embodiment 39. The method of embodiment 38, wherein the maximumtemperature during heat treating is not greater than 100° C. above themelting temperature of the material of the thermoelectric body, such asnot greater than 70° C., or not greater than 50° C., or not greater than30° C., or not greater than 10° C.

Embodiment 40. The method of any one of embodiments 35-39, whereinembedding the at least one first porous metal structure and the at leastone second porous metal structure within the first outer region and thesecond outer region of the thermoelectric body is conducted by applyingpressure during or after heat treating.

Embodiment 41. The method of any one of embodiments 35-40, furthercomprising polishing an outer surface of the first and/or second outerregion after embedding the at least one first porous metal structureand/or the at least one second porous metal structure, wherein polishingis conducted by removing material from the first and/or second outerregion until portions of the first porous metal structure and/or secondporous metal structure reach the outer surface of the first outer regionand/or second outer region of the thermoelectric body.

Embodiment 42. The method of any one of embodiments 35-41, wherein thefirst metal layer is applied by electroplating.

Embodiment 43. The method of any one of embodiments 35-42, furthercomprising applying a second metal layer directly overlying the firstmetal layer, wherein the second metal layer includes a same metal as thefirst metal layer.

Embodiment 44. The method of embodiment 43, wherein the at least oneporous metal structure, the first metal layer, and the second metallayer include nickel.

Embodiment 45. The method of embodiment 44, wherein the at least oneporous metal structure, the first metal layer, and the second metallayer consist essentially of nickel.

Embodiment 46. The method of any one of embodiments 43-45, wherein thefirst metal layer has a different stress than the second metal layer.

Embodiment 47. The method of any one of embodiments 35-46, wherein thethermoelectric body is an n-type thermoelectric material.

Embodiment 48. The method of any one of embodiments 35-47, wherein thethermoelectric body comprises a material including lead telluride(PbTe).

Embodiment 49. The method of any one of embodiments 35-46, wherein thethermoelectric body comprises a p-type semiconductor material.

Embodiment 50. The method of embodiment 49, wherein the thermoelectricbody comprises a material including Te/Sb/Ge/Ag (TAGS).

Embodiment 51. The method of any one of embodiments 35-50, wherein thefirst contact structure comprises at least one first porous metalstructure embedded within a first outer region of the thermoelectricbody, and the second contact structure comprises at least one secondporous metal structure embedded within a second outer region of thethermoelectric body, the second outer region being opposite to the firstouter region.

Embodiment 52. The method of any one of embodiments 35-51, wherein thesecond contact structure has a same structure as the first contactstructure and is concurrently formed with the first contact structure.

Embodiment 53. The method of any one of embodiments 35-51, wherein thesecond contact structure has a different structure than the firstcontact structure.

Embodiment 54. The method of embodiment 53, wherein the second contactstructure does not include a porous metal structure.

Embodiment 55. The method of embodiment 54, wherein the second contactstructure includes at least one metal layer.

Embodiment 56. The method of embodiment 55, wherein the second contactstructure includes four nickel layers.

Embodiment 57. The method of any one of embodiments 35-56, wherein thethermoelectric body comprises before heat treating at least oneprovisional metal layer directly overlying the first outer region and/orthe second outer region of the thermoelectric body, and heat treatingand partial melting of the first outer region and/or second outer regioncausing a chemical reaction of the at least one provisional metal layerwith a material of the thermoelectric body.

Embodiment 58. The method of embodiment 57, wherein the at least oneprovisional metal layer has a thickness of at least 1 micron and notgreater than 7 microns.

Embodiment 59. The method of embodiments 57 or 58, wherein the at leastone provisional metal layer includes two metal layers within one outerregion.

Embodiment 60. The method of any one of embodiments 57-59, wherein theat least one provisional metal layer includes nickel.

Embodiment 61. The method of any one of embodiments 57-60, wherein theat least one provisional metal layer comprises two provisional nickellayers.

Embodiment 62. The method of embodiment 61, wherein the two provisionalnickel layers include a first nickel layer directly overlying the outerregion of the thermoelectric body having a thickness of at least 20 nmand not greater than 1 micron, and a second provisional nickel layerdirectly overlying the first provisional nickel layer having a thicknessof at least 1 micron and not greater than 6 microns.

Embodiment 63. The method of embodiment 62, wherein the firstprovisional nickel layer has a higher stress than the second provisionalnickel layer.

Embodiment 64. A method of forming a first contact structure and asecond contact structure on a thermoelectric body, comprising:

-   -   providing an arrangement, the arrangement comprising in the        following order:        -   at least one first porous metal structure;        -   a thermoelectric body;        -   at least one second porous metal structure;    -   placing the arrangement in a furnace, the furnace comprising        induction heating elements;    -   induction heating the at least one first porous metal structure        and the at least one second porous metal structure, wherein heat        from the at least one first porous metal structure and the at        least one second porous metal structure causes a partial melting        and softening of a first outer region and a second outer region        of the thermoelectric body, respectively;    -   embedding the at least one first porous metal structure at least        partially within the first outer region of the thermoelectric        body to form an embedded first porous metal structure and        embedding the at least one second porous metal structure at        least partially within the second outer region of the        thermoelectric body to form an embedded second porous metal        structure; and    -   applying at least one metal layer on the first outer region and        at least one metal layer on the second outer region of the        thermoelectric body, wherein the at least one metal layer is in        direct contact with the first embedded porous metal structure        and with the second embedded porous metal structure.

Embodiment 65. The method of embodiment 64, wherein the arrangementfurther comprises a first induction heat absorber layer surrounded by afirst and second heat spreading layer, and a second induction heatabsorber layer surrounded by a third and fourth heat spreading layer,the arrangement having the following order:

-   -   a first heat spreading layer;    -   a first heat induction heat absorber layer;    -   a second heat absorber layer;    -   the at least one first porous metal structure;    -   the thermoelectric body;    -   the at least one second porous metal structure;    -   a third heat spreading layer;    -   a second induction heat absorbing layer; and    -   a fourth heat spreading layer.

Embodiment 66. The method of embodiments 64 or 65, wherein embedding theat least one first porous metal structure and the at least one secondporous metal structure is conducted by compressing the arrangementduring or after induction heating.

Embodiment 67. The method of any one of embodiments 64-66, whereininduction heating is conducted by a first heat treatment, the first heattreatment comprising heating the at least one first porous metalstructure and the at least one second porous metal structure for atleast 40 seconds and no longer than 160 seconds at a temperature of 120°C. to 180° C. followed by a second heat treatment, the second heattreatment comprising heating the at least one first and the at least onesecond porous metal structure and for at least 5 second and not longerthan 20 seconds at a maximum temperature of at least a meltingtemperature of the thermoelectric body and not greater than 100° C.above the melting temperature.

Embodiment 68. The method of embodiment 67, wherein induction heating isconducted by heating the at least one first porous metal structure andthe at least one second porous metal structure to a maximum temperaturenot greater than 50° C. above the melting temperature of thethermoelectric material.

Embodiment 69. The method of any one of embodiments 64-68, furthercomprising polishing the thermoelectric body after embedding the atleast one first porous metal structure and the at least one secondporous metal structure and before applying the at least one first metallayer, wherein polishing is conducted until the at least one firstporous metal structure and the at least one second porous metalstructure reach an outer surface of the first outer region and an outersurface of the at least one second outer region, respectively.

Embodiment 70. The method of any one of embodiments 64-69, whereinapplying the at least one first metal layer comprises applying a firstmetal layer and a second metal layer, the second metal layer directlyoverlying the first metal layer.

Embodiment 71. The method of embodiment 70, wherein the at least onfirst porous metal structure, the at least one second porous metalstructure, the first metal layer, and the second metal layer includenickel.

Embodiment 72. The method of embodiment 71, wherein the at least onfirst porous metal structure, the at least one second porous metalstructure, the first metal layer, and the second metal layer consistessentially of nickel.

Embodiment 73. The method of any one of embodiments 70-72, wherein thefirst metal layer has a different phase than the second metal layer.

Embodiment 74. The method of embodiment 73, wherein the first metallayer has a different stress than the second metal layer.

Embodiment 75. The method of any one of embodiments 67-74, whereininduction heating is controlled by measuring an electric current flowingthrough coils of an induction heater.

Embodiment 76. The method of embodiment 75, wherein induction heating isstopped by measuring an increase of the electric current of 3-5% duringthe second heat treatment.

Embodiment 77. An induction heating system comprising:

-   -   a furnace chamber comprising a non-magnetic and non-conductive        furnace wall;    -   an induction heating device including least one induction        heating coil surrounding an outer side of the furnace wall in a        length direction (z) of the furnace chamber; and    -   a holding and pressing construction;    -   wherein the holding and pressing construction is designed to        hold an arrangement to be placed within the furnace chamber, and        the holding and pressing construction can apply a pressure on a        proximal end and a distal end of the arrangement in the length        direction of the chamber.

Embodiment 78. The induction heating system of embodiment 77, furthercomprising a temperature sensor designed for measuring a temperature ofa layer of the arrangement.

Embodiment 79. The induction heating system of embodiment 78, whereinthe temperature sensor is an infrared temperature sensor.

Embodiment 80. The induction heating system of any one of embodiments77-79, further comprising an inlet and an outlet for applying acontrolled flow of an inert gas through the furnace chamber.

Embodiment 81. The induction heating system of any one of embodiments77-80, wherein a distance d_(i) of the induction heating coil to theouter side of the furnace wall ranges from 0 mm to 10 mm.

Embodiment 82. The induction heating system of embodiment 81, whereinthe distance d_(i) is at least 0.5 mm and not greater than 2 mm.

Embodiment 83. The induction heating system of embodiment 82, whereinthe distance d_(i) is 1.5 mm

Embodiment 84. The induction heating system of any one of embodiments77-83, wherein the at least one heating coil is hollow and adapted forpassing an air flow through the at least one heating coil duringoperation of the induction heating system.

Embodiment 85. The induction heating system of any one of embodiments77-84, wherein the holding and pressing construction is designed toapply a pressure of at least 5 psi and not greater than 15 psi on theinserted arrangement.

Embodiment 86. The induction heating system of any one of embodiments77-85, wherein the induction heating system further comprises a controlunit and an induction heating device.

Embodiment 87. The induction heating system of embodiment 86, whereinthe control unit is connected to the induction heating device and to thetemperature sensor.

Embodiment 88. The induction heating system of embodiments 86 or 87,wherein the control unit is adapted for regulating a desired currentfrequency and heating time for operating the at least one inductionheating coil.

Embodiment 89. The induction heating system of any one of embodiments77-88, wherein the induction heating system is adapted for varying acurrent frequency during induction heating.

Embodiment 90. The induction heating system of embodiment 89, whereinthe current frequency is at least 80 kHz, or at least 100 kHz, or atleast 200 kHz.

Embodiment 91. The induction heating system of embodiments 89 or 90,wherein the current frequency is not greater than 10 MHz, or 1 MHz or500 kHz.

Embodiment 92. The induction heating system of any one of embodiments86-91, wherein the induction heating system is adapted to measure anelectric current flow through the at least one heating coil.

Embodiment 93. The induction heating system of embodiment 92, whereinthe electric current is observed by the control unit, and the controlunit is configured to stop induction heating related to a pre-determinedelectric current increase within the at least one heating coil.

Embodiment 94. The induction heating system of any one of embodiments77-93, further comprising an ampere meter adapted for measuring anelectric current flow of an induction heating coil circuit duringoperation of the induction heating system.

Embodiment 95. The induction heating system of embodiment 94, whereinthe ampere meter is connected to the control unit.

Embodiment 96. The induction heating system of embodiment 95, whereinthe electric current is observed by the control unit, and the controlunit is configured to stop induction heating related to a pre-determinedelectric current increase within the at least one heating coil.

Embodiment 97. The induction heating system of embodiment 96, whereinthe control unit is configured to monitor current values obtained fromthe ampere meter and to stop induction heating according to apre-determined electric current increase within the heating coilcircuit.

Embodiment 98. The induction heating system of embodiment 97, whereinthe pre-determined electric current increase is 3-5% compared to acurrent flow when reaching a pre-determined base temperature recorded bythe temperature sensor.

Embodiment 99. The induction heating system of any one of embodiments77-98, wherein the induction heating system is designed for conductinginduction heating of an inserted arrangement up to a temperature of1200° C.

EXAMPLES

The following non-limiting examples illustrate the present invention.

Example 1

Preparing of a Thermoelectric Element Comprising a Thermoelectric BodyIncluding a p-Type TAGS with Embedded Nickel Mesh.

A round thermoelectric body including a p-type TAGS material and havinga diameter of 20 mm and a thickness of 2 mm was polished on bothsurfaces with a mechanical polisher containing an 800 grits polishingpad to obtain a smooth outer surface having a surface roughness between10 to 15 microns.

Thereafter, an arrangement was assembled placing the TAGS body in thecenter of the arrangement. The arrangement had the following layeredstructure: a first graphite heat spreading layer (71), an induction heatabsorber layer (72), a second graphite heat spreading layer (73), twonickel meshes (74), the above-described TAGS thermoelectric body (75);two further nickel meshes (76), a third graphite heat spreading layer(77), a second induction heat absorbing layer (78); and a fourthgraphite heat spreading layer (79), see also FIG. 7. Each of the twonickel meshes had a mesh count of 350 mesh/inch, an average wirediameter of 30 microns, and a thickness of about 40 microns, leading toa total thickness of 80 microns nickel mesh on each outer region of thethermoelectric body. The inner heat spreading layers (i.e., second andthird heat spreading layers 73 and 77) had a thickness of 0.5 mm, andthe outer heat spreading layers (i.e., the first and fourth heatspreading layers 71 and 79) had a thickness of 1 mm. The two inductionheat absorbing layers (72 and 78) included each one nickel mesh having athickness of 40 microns, which was of the same type of nickel mesh asplaced next to the outer regions of the TAGS body (74 and 76).

The arrangement was placed in a furnace designed for induction heating,as illustrated in FIG. 8. The arrangement (86) was fixed within thefurnace chamber (81) by the holding and pressing construction (85) and apressure of about 0.05 MPa (8 psi) was applied from the top and thebottom on the arrangement.

After the arrangement was placed in the furnace chamber, an argon gas(95% Argon:5% Hydrogen) was led through the chamber for about 2 minutesto provide oxygen-free conditions. The flow rate of the argon gasthrough the furnace was about 50 ml/min. Thereafter, induction heatingwas conducted by heating the induction heating elements (herein alsocalled tooling) to a temperature of 160° C. for 140 seconds, followed byincreasing the temperature of the tooling to 320° C. for a time of about6-8 seconds. The tooling was positioned at a distance of 1.5 mm next tothe wafer.

The use of the induction heating elements allowed for rapid heating ofthe nickel mesh to a temperature of about 630° C., which is close to themelting temperature of the TAGS body. The applied current frequency wasabout 100 kHz. The argon gas flow was maintained at the same flow rateduring the whole processing within the chamber.

The induction heating caused a melting of the first and second outerregion of the TAGS body, and an embedding of the metal meshes within theouter regions while the arrangement stayed under the same pressure.

After cooling to a temperature of about 70° C., the arrangement wastaken out of the furnace chamber.

The thermoelectric body containing the embedded nickel meshes wassubjected to mechanical polishing using 600 and 800 grit lapping padsuntil the metal mesh reached the outer surface of the TAGS body on bothsides. The amount of TAGS material removed from the surface was about 10microns until the nickel mesh reached the outer surface.

Thereafter, the polished TAGS body including the embedded fiber mesheswas subjected to a first nickel electroplating to deposit a first nickellayer having a thickness of about 50 nm. The electroplating of the firstnickel layer was conducted using the plating system and conditionsdescribed below, wherein the plating bath was adjusted to a pH of about8.0.

After electroplating the first nickel layer, the plating bath waschanged, by using a bath having the same ingredients but an adjusted pHof about 4.0, and a second nickel electroplating was conducted todeposit a second nickel layer having a thickness of about 10 microns.

An optical image of the thermoelectric TAGS body with two embeddednickel meshes within each of the first and second outer regions can beseen in FIG. 6. It can be seen that the metal meshes (61 a, 61 b) werecompletely embedded within the outer regions of the TAGS body, and thenickel plated layers (65, 66) were in direct contact with the embeddedmetal meshes (61 a, 61 b), respectively. The depth of the embeddednickel meshes within the thermoelectric body was about 350 microns.

After the electroplating of the second nickel layer, a silver layerhaving a thickness of about 15 microns was deposited on top of thesecond nickel layer.

Nickel Electroplating

The plating system contained a nickel anode, and a 400 ml plating bath,into which a plurality of four thermoelectric bodies, herein also calledwafers, were inserted. The plating bath contained nickel sulphamate andhad a temperature during the plating at laboratory room temperature of23-25° C. The four wafers were placed parallel to each other andconnected to a voltage source. Between each wafer and the voltage sourcewas placed a precision resistor. The electroplating was conducted underthe condition that the plating bath had a high resistance of about 500Ohm, while the wafers had a low resistance. The resistance of the waferswas in a range of 0.1 to 0.5 mOhm and was more than 10,000 times lowerthan the resistance of the precision resistors, such that the followingequation (1) applied: r×10,000<R (1), with R being the resistance of theprecision resistor, and r being the resistance of the wafer.

By using the above-described plating system, it was possible to formuniform layers on non-uniform substrates (wafers). For example, ifwafers had a resistance span of 0.1 to 0.5 mOhm, uniform nickel layersof a controlled thickness between 1-20 microns could be formed, withminor thickness variation.

Example 2

Preparing of a Thermoelectric Element Comprising a Thermoelectric BodyIncluding PbTe with Embedded Nickel Mesh.

A round thermoelectric body including n-type doped lead telluride (PbTe)having a diameter of 20 mm and a wafer thickness of 2 mm, was polishedon both surfaces using a mechanical polisher with an 800 grits polishingpad to obtain a smooth outer surface having a surface roughness between10 to 15 microns.

After the polishing, the surface of the PbTe body was etched using a 2:1water to nitric acid treatment solution for 1 minute in order to removeabout 2-10 microns from the outer surface and to activate the surfacetowards nickel plating. Following the etching, the surface was cleanedwith de-ionized water and dried with dry nitrogen spray at roomtemperature.

Thereafter, the polished PbTe body was subjected to nickelelectroplating to deposit a first provisional nickel layer having athickness of about 50 nm, wherein the plating bath was adjusted to a pHof about 8.0. After electroplating the first provisional nickel layer, asecond provisional nickel layer having a thickness of 5 microns waselectroplated directly over the first provisional nickel layer. Theplating bath for plating the second provisional nickel layer had a pH of4 but was otherwise the same as for plating the first provisional nickellayer.

Thereafter, an arrangement was assembled placing the thermoelectric bodyincluding the two provisional nickel layers in the center of thearrangement. The arrangement had the same layered structure as describedin Example 1, except that the thickness of each of the four graphiteheat spreading layers was 0.5 mm.

The arrangement was placed in a furnace designed for induction heating,as illustrated in FIG. 8. The arrangement (86) was fixed within thefurnace chamber (81) by the holding and pressing construction (85) and apressure of about 8 psi was applied from the top and the bottom on thearrangement.

After the arrangement was placed in the furnace chamber, an argon gas(Argon 95%:Hydrogen 5%) was led through the furnace chamber for 2minutes to provide oxygen-free heating conditions, before starting theconduction heating with a flow rate of 50 ml/min. The argon gas flow wasmaintained during the induction heating and cooling after the heating.Induction heating was conducted by heating the tooling to a temperatureof 160° C. and holding the temperature for about 150 seconds, followedby increasing the tooling temperature to 455° C. and holding thetemperature for a time of 6-8 seconds. The applied current frequency was100 kHz.

The induction heating caused a heating of the metal meshes to atemperature of about 920° C., which caused melting of the first andsecond outer regions of the PbTe body, and a complete embedding of themetal meshes within the outer regions while the submitted pressure onthe arrangement was maintained. The provisional nickel layers that wereapplied on the thermoelectric body before induction heating reacted withthe melted PbTe material and could not be observed anymore afterembedding the nickel meshes. After the arrangement has cooled down to atemperature of about 70° C., the arrangement was removed from theinduction heating system and the thermoelectric body containing theembedded nickel meshes was subjected to mechanical polishing using 600and 800 grit lapping paper until the metal mesh reached the outersurface of the PbTe body on both sides. The amount of PbTe materialremoved from the surface was about 30 microns until the nickel meshreached the outer surface.

Thereafter, the polished PbTe body was subjected to a first nickelelectroplating to deposit a first nickel layer having a thickness ofabout 50 nm. The electroplating of the first nickel layer was conductedusing the plating system and conditions described in Example 1, whereinthe plating bath was adjusted to a pH of about 8.0.

After electroplating the first nickel layer, the plating bath waschanged, by using a bath having the same ingredients but an adjusted pHof about 4.0, and a second nickel electroplating was conducted todeposit a second nickel layer having a thickness of about 10 microns.

FIG. 5 shows an optical image of the thermoelectric PbTe body containingtwo embedded nickel meshes (51 a) within the first outer region and twoembedded nickel meshes (51 b) within the second outer region, andfurther two plated nickel layers on each side (55, 56). It can befurther seen in FIG. 5 that the metal meshes were completely embeddedwithin the first outer region and the second outer region. The depth ofthe embedded meshes within the thermoelectric body was about 200microns. The provisional nickel layers applied before the inductionheating on the thermoelectric body cannot be observed in FIG. 5. Notbeing bound to theory, it is assumed that the provisional nickel layerschemically reacted with the melted PbTe material of the outer regionsand were thereby consumed.

After electroplating of the second nickel layer, a silver layer having athickness of about 15 microns was deposited on top of the second nickellayer deposited from an AgCN bath.

The two nickel layers and the silver layer were all applied concurrentlyon both surfaces of the PbTe body, which are herein called a contactstructure (CS01) and a second contact structure (CS02), such that eachcontact structure contained two nickel meshes and two nickel layers.

Example 3

Preparing of a Thermoelectric Element Comprising a Thermoelectric BodyIncluding PbTe.

A thermoelectric element was made the same way as described in Example2, except that no provisional nickel layers were applied on thethermoelectric PbTe body before induction heating.

It could be observed that the depth of the embedded nickel meshes wasabout the same as in Example 2, however, the strength of the contactstructure was not as good as the contact structure described in Example2. Not being bound to theory, it appears that the provisional nickellayers chemically reacted with the softened PbTe material and that thereaction product provides a stronger hold of the embedded nickel meshesthan the PbTe material alone.

Example 4

Preparing of a Thermoelectric Element Comprising a Thermoelectric BodyIncluding a p-Type TAGS with Embedded Nickel Foam.

The thermoelectric element including a p-type TAGS was prepared the sameway as in Example 1, except that the two metal meshes on each side werereplaced by a metal foam on each side. The metal foam had a thickness ofabout 100 microns. The metal foam was originally a nickel foam having athickness of about 1.0-1.6 mm with a porosity of >95 vol % and 80-110pores per inch (average hole diameter of 0.25 mm) and a density of 0.403g/cm³ and was pressed down before use to a thickness of about 0.1 mm(100 microns) and a density of 3.3 g/cm³.

A further difference to Example 1 was the controlling of the inductionheating. When using the metal foam induction heating was conducted byheating the tooling to a temperature of 160° C. and holding thetemperature for 140 seconds, followed by increasing the toolingtemperature to 320° C. and holding the temperature at 320° C. until theelectric current flowing through the induction coils increased by 3-5%in comparison to the current flow detected when reaching the 320° C.temperature plateau. The electric current when reaching the 320° C.(_(ATmax-b)) in the tooling was about 8 A and was stopped when reachinga value of 8.3 A. Not being bound to theory, the increase in the currentflow can be an indication of the reaction of the nickel foam with theTAGS body when being embedded within the outer regions; and can berelated to a drop in the electromagnetic permeability of the nickel foamcaused by the reaction. Stopping the heating at an increase of theelectric current by 0.3 A corresponded to a time of about 6-8 seconds atthe maximum tooling temperature of 320° C. Observing the increase in thecurrent and stopping the heat treatment by detecting the currentincrease of 0.3 A can have the advantage of being highly sensitivecorresponding to the reaction of the nickel foam with the TAGS, and mayprevent unwanted damage of the TAGS by a prolonged heating time. Thetooling was positioned at a distance of 1.5 mm next to the wafer. Theuse of the induction heating elements allowed for a rapid heating of thenickel foam to a temperature of about 630° C., which is close to themelting temperature of the TAGS body. The applied current frequency wasabout 100 kHz.

The argon gas flow was maintained at the same flow rate during the wholeprocessing within the chamber.

After the induction heating, the obtained thermoelectric body containingthe embedded nickel foam on each side was subjected to mechanicalpolishing using 600 and 800 grit lapping pads until the metal foamreached the outer surface of the TAGS body on both sides. The amount ofTAGS material removed from the surface was about 10-80 microns until thenickel foam reached the outer surface.

Thereafter, the polished TAGS body including the embedded metal foamswas subjected to nickel electroplating, the same way as described inExample 1, by applying a first and a second nickel layer.

After the electroplating of the two nickel layers, a silver layer havinga thickness of about 15 microns was deposited on top of the secondnickel layer, the same way as in Example 1. An optical microscope imageof the thermoelectric TAGS body with embedded nickel foam in one of theouter regions can be seen in FIGS. 10A and 10B. It can be seen that thenickel foam (102) is embedded within the TAGS body (103) and partiallyreacted with the TAGS, above the embedded nickel foam are theelectroplated nickel layers (104), followed by the electroplated silverlayer (105).

Example 5

Preparing of a Thermoelectric Element Comprising a Thermoelectric BodyIncluding PbTe with Embedded Nickel Foam.

The thermoelectric element including a PbTe was prepared the same way asin Example 2, except that the two metal meshes on each side werereplaced by a metal foam on each side. The metal foam had a thickness ofabout 100 microns. The metal foam was originally a nickel foam having athickness between 1.0-1.6 mm with a porosity of >95 vol % and 80-110pores per inch (average hole diameter of 0.25 mm) and a density of 0.403g/cm³ and was pressed down before use to a thickness of about 0.1 mm(100 microns) to a density of 3.3 g/cm³.

A further difference to Example 2 was the induction heating. When usingthe metal foam, induction heating was conducted by heating the toolingto a temperature of 160° C. and maintained for 150 seconds, followed byincreasing the tooling temperature to 455° C. and holding thetemperature at 455° C. until the electric current flow through theinduction coil increased by 3-5% in comparison to the current flowdetected when reaching the 455° C. temperature plateau. Specifically,the current was about 9 A when reaching the tooling temperature of 455°C. (A_(Tmax-b)) and was stopped when reaching a value of 9.3 A(A_(Tmax-b)+0.3 A). Not being bound to theory, the increase in thecurrent flow can be an indication of a reaction of the nickel foam withthe PbTe; and may be related to a drop in the electromagneticpermeability of the nickel foam when reacting with the PbTe material.Stopping the heating at 9.3 A (herein also indicated as A_(S)),corresponding to a time of about 6 seconds at the maximum temperature of455° C. Observing the increase in the electric current and stopping theheat treatment by detecting the current increase of 0.3 A can have theadvantage of being highly sensitive corresponding to the reaction of thenickel foam with the PbTe, and may prevent unwanted damage of the PbTeby a prolonged heating time.

The induction heating caused a heating of the metal foam to atemperature of about 920° C., which caused a melting of the first andsecond outer regions of the PbTe body, and a complete embedding of themetal foams within the outer regions while the submitted pressure on thearrangement was maintained. The provisional nickel layers that wereapplied on the thermoelectric body before induction heating reacted withthe melted PbTe material and could not be observed anymore afterembedding the nickel meshes.

The argon gas flow was maintained at the same flow rate during the wholeprocessing within the chamber.

The obtained thermoelectric body containing the embedded nickel foam wassubjected to mechanical polishing using 600 and 800 grit lapping padsuntil the metal foam reached the outer surface of the PbTe body on bothsides. The amount of PbTe material removed from the surface was about10-80 microns until the nickel mesh reached the outer surface.

Thereafter, the polished PbTe body including the embedded metal foamswas subjected to nickel electroplating, the same way as described inExample 1, by applying a first and a second nickel layer.

After electroplating the nickel layers, outer silver layers wereelectroplated over the second nickel layers on each side the same way asdescribed in Example 2.

FIGS. 11A and 11B show optical microscope images of the producedmulti-layer contact structure on one side or the thermoelectric element.Region (112) is related to the nickel foam which partially reacted withthe PbTe (113), followed by electroplated nickel layers (114) and theelectroplated silver layer (115).

Example 6

Testing of the Life-Time/Performance of the Thermoelectric Elements.

The thermoelectric elements of Examples 1, 2, 4, and 5 were subjected tohigh temperature cycles and the maximum power at the peak temperaturewas measured during each cycle. The lifetime of a thermoelectric elementwas defined as the number of cycles counted when the maximum powermeasured decreased less than 15% as compared to the maximum powermeasured during the first cycle.

The thermoelectric elements of Examples 1, 2, 4, and 5 had an about 500times higher lifetime than comparative thermoelectric elements that weremade using the same thermoelectric bodies as in Examples 1 to 3, buthaving a multi-layer contact layer structure of a nickel (1micron)/silver (8 microns)/indium (5 microns), and without heattreatment.

In comparison to a comparative thermoelectric element having the samethermoelectric body but, on each side, a four-layer nickel/silver layercontact structure, such as (Ni 50 nm/Ni 15 microns/Ni 50 nm/Ni 15microns/Ag 15 microns), and no embedded nickel mesh, the thermoelectricelements of Examples 1, 2, 4 and 5 had a 40 to 60 time higher life-time.

What is claimed is:
 1. A thermoelectric element comprising: athermoelectric body, a first contact structure, and a second contactstructure, wherein the first contact structure comprises at least onefirst porous metal structure and at least one metal layer, wherein theat least one first porous metal structure is at least partially embeddedwithin a first outer region of the thermoelectric body, and the at leastone metal layer is overlying an outer surface of the first outer regionof the thermoelectric body and in direct contact with the at least onemetal mesh.
 2. The thermoelectric element of claim 1, wherein the atleast one metal layer comprises a first metal layer and a second metallayer, and wherein each of the at least one first porous metalstructure, the first metal layer, and the second metal layer include thesame metal.
 3. The thermoelectric element of claim 2, wherein each ofthe at least one first porous metal structure, the first metal layer,and the second metal layer comprise nickel.
 4. The thermoelectricelement of claim 3, wherein each of the at least one first porous metalstructure, the first metal layer, and the second metal layer consistessentially of nickel.
 5. The thermoelectric element of claim 1, whereinthe at least one first porous metal structure has a thickness of atleast 30 microns and not greater than 175 microns.
 6. The thermoelectricelement of claim 1, wherein at least 90 vol % of the at least one firstporous metal structure is embedded within the first outer region of thethermoelectric body.
 7. The thermoelectric element of claim 6, the atleast one first porous metal structure is fully embedded within thefirst outer region of the thermoelectric body.
 8. The thermoelectricelement of claim 1, wherein the at least one first porous metalstructure includes at least one metal mesh, or at least one metal foam,or any combination thereof.
 9. The thermoelectric element of claim 1,wherein the first metal layer has a different stress than the secondmetal layer.
 10. The thermoelectric element of claim 1, wherein thesecond contact structure is the same as the first contact structure andthe second contact structure is attached to the thermoelectric body at asecond outer region of the thermoelectric body, the second outer regionbeing opposite to the first outer region.
 11. The thermoelectric elementof claim 1, wherein the second contact structure is different than thefirst contact structure.
 12. The thermoelectric element of claim 1,wherein the thermoelectric body comprises a material including leadtelluride (PbTe) or a material including Te/Sb/Ge/Ag (TAGS).
 13. Thethermoelectric element of claim 1, wherein the thermoelectric element isadapted for converting heat energy from a heat source to electricalenergy, the heat source having a temperature of at least 100° C. and notgreater than 650° C.
 14. A method of forming a contact structure on athermoelectric body, comprising: providing a thermoelectric body havinga first outer region and a second outer region, the second outer regionbeing opposite to the first outer region; heat treating the first and/orthe second outer region of the thermoelectric body, wherein heattreating causes a partial melting of the first and/or the second outerregion and forming of a softened first outer region and/or a softenedsecond outer region; embedding at least one first porous metal structurewithin the softened first outer region and/or at least one second porousmetal structure within the second outer region; cooling and solidifyingthe softened first outer region and/or the softened second outer regionto form a first outer region comprising at least one first embeddedporous metal structure and/or a second outer region comprising at leastone second embedded porous metal structure; applying at least one metallayer overlying an outer surface of the first outer region and/or atleast one metal layer overlying an outer surface of the second outerregion, wherein the at least one metal layer is in direct contact withthe at least one first embedded porous metal structure and/or the atleast one metal layer is in direct contact with the at least one secondembedded porous metal structure.
 15. The method of claim 14, whereinheat treating is conducted by induction heating.
 16. The method of claim14, wherein the at least one metal layer comprises a first metal layerand a second metal layer, the first metal layer being in direct contactwith the at least one first embedded metal structure and/or the at leastone second embedded metal structure, and the second metal layer isdirectly overlying the first metal layer.
 17. The method of claim 16,wherein the at least one first and/or second porous metal structurehaving, the first metal layer, and the second metal layer consistessentially of nickel.
 18. A method of forming a first contact structureand a second contact structure on a thermoelectric body, comprising:providing an arrangement, the arrangement comprising in the followingorder: at least one first porous metal structure; a thermoelectric body;and at least one second porous metal structure; placing the arrangementin a furnace, the furnace comprising induction heating elements;induction heating the at least one first porous metal structure and theat least one second porous metal structure, wherein heat from the atleast one first porous metal structure and the at least one secondporous metal structure causes a partial melting and softening of a firstouter region and of a second outer region of the thermoelectric body,respectively; embedding the at least one first porous metal structure atleast partially within the first outer region of the thermoelectric bodyto form an embedded first porous metal structure and embedding the atleast one second porous metal structure at least partially within thesecond outer region of the thermoelectric body to form an embeddedsecond porous metal structure; and applying at least one metal layer onthe first outer region and at least one metal layer on the second outerregion of the thermoelectric body, wherein the at least one metal layeris in direct contact with the first embedded porous metal structure andwith the second embedded porous metal structure.
 19. The method of claim18, wherein the arrangement further comprises a first induction heatabsorber layer surrounded by a first and second heat spreading layer,and a second induction heat absorber layer surrounded by a third andfourth heat spreading layer, the arrangement having the following order:a first heat spreading layer; a first heat induction heat absorberlayer; a second heat absorber layer; the at least one first porous metalstructure; the thermoelectric body; the at least one second porous metalstructure; a third heat spreading layer; a second induction heatabsorbing layer; and a fourth heat spreading layer.
 20. The method ofclaim 18, wherein the at least one first porous metal structure, the atleast one second porous metal structure, and the at least one metallayer comprise nickel.